Automated transaction machines, and particularly automated teller machines (ATMs) used to carry out banking transactions, are operated using electrical circuitry and components including motors, transformers, relays, solenoids and other actuating devices, all of which generate unwarranted electrical signals or "noise".
One important ATM function is dispensing and receiving sheets. Such sheets may be of several types. A common type of sheet dispensed is currency in the form of currency notes or bills. On occasion two or more bills may adhere to each other due to the surface condition of the bills or humidity or other weather conditions. It is desirable for this condition to be detected before the bills are dispensed. A similar condition may occur in currency receiving machines. Two or more bills adhering together introduces errors into the currency receiving process.
Mechanical thickness detection methods have been developed, but variations in surface characteristics of bills which have been in circulation as compared to new bills make thickness detection for double bills difficult. If detection in a dispensing function is not sensitive enough, multiple bills may be dispensed and a loss incurred by the ATM operator. If detection is too sensitive, thicker single bills will be diverted and not dispensed, causing the ATM to require restocking more frequently than otherwise necessary.
Electrical and optical detection methods are affected by the electrical noise in the ATM environment. Such noise affects the sensitivity at which electrical and optical methods can operate. Signal strength must be high enough that it can be detected above the electrical noise floor in the ATM. Increasing signal strength requires higher power operation. Components with higher ratings are required to operate at higher power without deteriorating sensitivity and to avoid operational problems such as signal saturation.
Radiation type sheet thickness detection devices may have their accuracy adversely affected by differences in sheet coloration. For example, a dark color sheet usually absorbs more radiation than lighter color sheets. Different materials used in currencies of different countries have different radiation absorption properties. This can make it difficult to distinguish between single and multiple sheets. This presents challenges for automated transaction machines which must distinguish between single and multiple sheets having varied radiation absorption and reflectance properties.
Thus there exists a need for an improved sheet thickness detecting device and method for distinguishing between single and multiple sheets dispensed by an automated transaction machine.